package com.string;

public class Solution06 {
    public int strStr(String haystack, String needle) {
        int[] next = new int[needle.length()];
        getNext(next, needle);

        int j = 0;
        for (int i = 0; i < haystack.length(); i++) {
            while (j > 0 && haystack.charAt(i) != needle.charAt(j)) j = next[j - 1];

            if (haystack.charAt(i) == needle.charAt(j)) j++;

            if (j == needle.length()) return i - needle.length() + 1;
        }
        return -1;
    }

    private static void getNext(int[] next, String s) {
        int j = 0;
        next[0] = 0;
        for (int i = 1; i < s.length(); i++) {
            while (j > 0 && s.charAt(i) != s.charAt(j)) j = next[j - 1];

            if (s.charAt(i) == s.charAt(j)) j++;
            next[i] = j;
        }
    }
}
